1. Field of the Invention
The present invention relates to a production scheduling management system and a method of managing production scheduling, and in particular to a technique for minimizing influences on lot processing schedules.
2. Description of Related Art
A plurality of lots each containing a plurality of silicon wafers are present in a semiconductor production line in which each lot is transported and processed as a unit. Semiconductors are subjected to several hundreds of processes, to provide final products. The production scheduling for a semiconductor production line is performed by tracking the current position of each of the lots in the production line.
In each process of semiconductor manufacturing, it is determined which lot or lots is/are waiting for processing at the current point of time. Also, a production management system manages the expected date and desired date (delivery date) on which processing of all products is expected to be completed.
FIG. 1 is a schematic view useful in explaining a related technology of production scheduling management method. Suppose some lots, which have been processed in the previous process step, are now ready to be processed in the next process step. A CR (Clean Room) operator in charge of each process selects a certain number of lots that can be processed at a time, from a plurality of lots that are waiting for processing, and executes the process on the selected lots. Where a CR operator A finishes processing some lots, as shown in FIG. 1 by way of example, the lots are transported or moved to a job location managed by a CR operator B in charge of the next process. The CR operator B then determines which lot or lots is/are to be processed first, based on the lot delivery date and other information.
Each CR operator selects the lot(s) to be processed next, based on the order in which the lots reach the relevant process managed by the operator, or on the order that is determined in terms of the delivery date of each lot under control of the production scheduling system. Based on these criteria, priority rating is given to the lots that are waiting for processing, namely, the lots waiting for processing are arranged in the order of priority in which processing of the lots is to be started, and the CR operator executes the process according to the order thus determined.
The production scheduling management method as described above, however, suffers from the following problems:
(1) The order of priority in which the process is executed is determined with respect to all of the lots that are waiting for processing. Namely, the priority rating does not involve lots that still remain in any one of the processes prior to the relevant process. In this case, if a higher-priority lot reaches the relevant process immediately after the process starts being executed, for example, the lot must be kept waiting for processing for a long time in spite of the fact that the higher priority is given to the lot, resulting in a delay in processing the lot.
(2) In a process step in which batch processing is employed, namely, where a process is executed on a batch of lots at a time, so-called charging is performed in which a processing machine or apparatus is charged with a plurality of lots (batch) that are to be processed under the same conditions, so that the batch of lots is processed at the same time. In this type of process, it is highly desirable to charge the processing machine with the maximum number of lots that are allowed to be set in the machine, so as to improve the performance or efficiency of the machine.
If the above-described charging is performed only with respect to the lots that are currently waiting for processing, however, the case as follows often arises: the process is executed while the processing machine has not been charged with the maximum permissible number of lots, and more lots that can be processed under the same conditions reach the relevant process immediately after the process starts being executed. In such a case, the efficiency of lot processing is considerably reduced or deteriorated.
(3) While the lots waiting for processing are considered as being in the order of priority in which the next processing is to be started, there is no concept of time with respect to these lots, namely, there is no limit to the time by which each lot should start being processed. In the meantime, routine or non-routine maintenance is performed on each manufacturing apparatus or machine, and such maintenance may cause a delay in the progress of lots that are to be processed by the apparatus. Since there is no limit to the time by which the lots waiting for processing should start being processed, the operator may inadvertently perform maintenance of the apparatus, thus causing a problem in carrying out lot processing schedules.
(4) The progress of lots may also be disturbed or impeded by faults, troubles, or other unexpected incidents of manufacturing apparatuses. Where such an incident causes a delay in the progress of lots, with a result being behind lot processing schedules, there arises a need to review and revise the lot processing schedules. Since it takes a great amount of time to reschedule the progress of lots, the schedules are less frequently reviewed for rescheduling, and the order of priority as described above may be inappropriately determined according to the delayed schedules.
The present invention was developed in the light of the situations as described above. It is therefore an object of the present invention to provide a production scheduling management system and method that enable preparations for production, such as production planning, to be accomplished with high efficiency, and properly carry out operations according to schedules, thereby to minimize influences on lot processing schedules. It is another object of the invention to provide a computer-readable storage medium containing such a production scheduling management method as (a) program(s).
To accomplish the above object, a production scheduling management system is provided, which comprises a production planning unit that receives production scheduling information including at least information on the delivery date of each lot, produces a production schedule of each lot, and outputs a production schedule; and a work scheduling unit that receives the production schedule and work scheduling information, produces a work schedule so as to fulfill the production schedule, while taking account of conditions of each machine and conditions of each lot, and generates at least one work schedule.
The order in which each lot starts being processed is determined in terms of time. Namely, the present production scheduling management system is characterized in that processing in each process step is scheduled with respect to lots that have not reached the relevant process step, as well as lots that are currently waiting for processing in this step. This enables the operator to be aware of the presence of a high-priority lot or lots that have not reached the process managed by the operator, and the time by which the high-priority lot(s) should start being processed in the process step. This arrangement avoids a situation in which the start of processing of the high-priority lots is delayed while other lots are being processed in the process step.
Since execution of each process is scheduled in terms of time, with respect to the lots that have not reached the relevant process step, as well as the lots waiting for processing, charging of the machine may be performed with high efficiency, taking account of the lots that have not reached the relevant process step, as well as the lots that are currently waiting for processing.
The present production scheduling management system has three or more scheduling units. For example, a short-range production scheduling unit may be provided so that the amount of lots processed in each step can be estimated, and maintenance works of each apparatus or machine can be scheduled to be conducted in such a period of time that does not affect the progress of lots. This avoids a delay in the lot processing schedule, which would otherwise occur when the operator inadvertently performs a maintenance work.
According to the production scheduling management system as described above, preparations, such as production planning, can be made with high efficiency, and scheduled works can be properly accomplished on time, while minimizing influences on the lot processing schedule.